Ceramic magnetic materials with high saturation-flux density



Patented Aug. 21 1951 UNITED CERAMIC MAGNETIC MATERIALS WITH HIGH SATURATION-FLUX DENSITY Ernst Mixers-Schoenberg, Metuchcn, N. J., as signor to Steatite Research Corporation, Keasbey, N. J., a corporation of Delaware N Drawing. Application May 26, 1949, Serial No. 95,581

4 Claims.

This invention relates to a ferromagnetic ceramic material with a high saturation-flux density and method of making the same.

An object of this invention is to provide a method of making a ceramic magnetic material with a high saturation-flux density.

Another object of the invention is to provide a ceramic magnetic material with a high saturation-flux density.

Another object of the invention is to provide a ceramic magnetic material with a relatively high Curie point and a high saturation-flux density, and process of making the same.

Another object of the invention is to provide a ceramic magnetic material with a relatively low temperature coefficient, a relatively high Curie point and a high saturation-flux density and a process of making the same.

Recently a number of ferrite compounds have been developed and described in the technical literature, i. e., ferromagnetic oxides of the general formula MFe2O4, where M represents a bivalent metal, as, for instance, manganese, copper or magnesium. Each of these ferrites which forms crystals of the same shape as the magnetite, F6304, has a different magnetic permeability, ohmic resistance, Curie point and magnetic losses. On the whole, these compounds or suitable mixtures of them, cover a range ofinitial permeability from very low figures below 30 up to high values of more than 1000, the ohmic resistance varying between to 10 ohms-cm. As a rough rule a high initial permeability in such compounds is found to be associated with a fairly low Curie point, while Curie temperatures above 200 C. are found to be related to a medium or a low initial permeability of several hundreds or less. Another relation has been found to exist between the initial permeability and the conductivity, namely, as the permeability increases the conductivity shows an increase likewise.

For some purposes a high initial permeability is desirable but according to the present invention it has been found that by sacrificing a certain amount of the high initial permeability property, other very valuable properties are obtained. It might be expected that higher Curie points could be obtained from compositions having a medium or low initial permeability but the particular composition employed in the present invention is very unusual in that it has a high saturation-flux density which exceeds that of the high permeability bodies.

The ferrite compounds of this invention have an initial permeability between 200 and 350, small magnetic losses over the frequency range of 60 cs. to about 10 mos, a Curie point of 250 C. or

2 higher, a temperature coefficient of 25 to 35% for C. temperature increase, measured on toroidal cores between room temperature and If the material is employed as a cylindrical core in an inductance coil instead of a toroidal core the temperature coefl'icient corresponding to the eifective ,u. of the core is lower in the range of about 5% per 100 C.

A material of this kind is formed as a compound of five (5) oxides, MgO, MnO, ZnO, mo and F8203, the mol ratio between the total of all bivalent oxides and the trivalent iron oxide being close to 1:1; the proportion between the single bivalent oxides lies within the limits ..05-.15 MgO:.2-.4= MnO:.3-.4 ZnO:.l5-.4 NiO. A peculiarity of these materials is the fact that they show a high saturation flux-density of at least 3750 up to more than 000 exceeding the saturation fiux-density of the high permeability bodies. The high saturation bodies are fired at fairlyhigh temperatures between Seger cones 7 and 10 and cooled in air, i. e. without applying a protective atmosphere.

The various components or compounds adapted to form the components of the final product during firing are combined in the proper proportions. For example, the manganese oxide component of the final product is preferably added in the form of manganese dioxide and when lithium oxide is employed as a component it is added in the form of the carbonate, etc. During firing these compounds are reduced to the required oxides. In the examples below the "mol ratio refers to the final product Whereas the composition refers to the mix before firing. The powders are preferably ground to a very fine particle size, for example, less than 0.010 m. m. The final pulverized mixed powder is wet with an aqueous binder which may be just ordinary water or may contain emulsified waxes or other plasticizers or binding agents. Enough of the aqueous binder is added to make the mix coherent when placed under pressure and the mix is thereafter molded. Any molding device such as a steel die or a ceramic extruding machine may be employed. After molding the articles are fired at Seger cones 7-10 and cooled. No special precautions are required during cooling.

The novel features characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying examples:

Example 1 The mix is ballmilled and moistened and plasticized by an addition of 4% of a wax-water emulsion. The wax-water emulsion contains 50% of wax. The mix is then molded by pressing and fired at about Seger-cone 9. 1 After firing the molded article is cooled in air at room temperature. The physical properties of this material are shown in the following table:

Initial permeability (1-3 mcs.) 300 Maximum permeability (D. C.) 900 Saturation flux-density (Gauss) 4200 Resistivity (ohm-cm., room temperature) 10 Curie point C 260 Temperature coefiicient of (toroid) 33% change from room temperature to 125 C.

Example 2 A mix is made up of the following components: M01 ratio:.l MgO: .2 MnO2A= ZnO :.3 N10: about 1 F6203.

Composition:

1.5 MgO 7.5 M1102 10.5 ZnO 12.5 NiO 68.0 FezOa The preparation and molding is done in the same way as mentioned in Example 1, firing at about Seger cone 10. After firing the molded article is cooled in air at room temperature. The physical properties are the following:

Initial permeability (l-3 mcs.) 230 Maximum permeability (D. C.) 1000 Saturation flux-density (Gauss) 4800 Resistivity (ohms-cm. room temperature) -1 10 Curie point C 260 Temperature coefiicient of (toroid) 28% change between room temperature and 125 C.

Example 3 A mix is made up of the following components: Mol ratio: .09 MgO:.4 MnO:.34 ZnO:.l7 NiO: about 1 F6203.

Composition:

1.5 MgO 13.5 MnOz 11.0 ZnO 5.0 NiO 69.0 F8203 The preparation and molding is done in the same way as mentioned in Example 1 with the firing temperature at about cone After firin the molded product is allowed to cool in air. The properties of the fired material are as follows:

Initial permeability (l-3 mos.) 220 Maximum permeability(D. C.) 850 Saturation flux-density (Gauss) 4000 Resistivity (ohms-cm, room temperature) 10 Curie point C 265 Temperature coeiiicient of (toroid) 32% change between room temperature and 125C.

These products are especially useful for transformer and inductance coils.

I claim:

1. A ferromagnetic ceramic material consisting mainly of iron oxide compounds of the magnetitetype, suitable for the use at frequencies between 60 cs. and about 10 mos. composed of the bivalent metal oxides MgO MnO, ZnO and MO and F6203 in the mol ratio of .05-.15 MgO:.2-.4 MnO:.3-.4 ZnO:.l5-.4 Nioiabout 1.0 FezOs, the total mol ratio of said bivalent metal oxides to F6203 being approximately 1:1 said material having a Curie point of at least 250 C., an initial permeability between 200 and 350, a saturation-flux density of at least 3750 and a temperature coemcient of a of 25 to 35% (measured on a toroid) between room temperature and C.

2. A process of making a ferromagnetic ceramic material having small magnetic losses over a frequency range of 60 cycles to 10 megacycles and a high saturation-flux density comprising the steps of grinding and mixing together cornponents adapted to yield after firing the bivalent metal oxides MgO, MnO, ZnO and MO and F6203 in the mol ratio of .05-.15 NIgOLZ-fl MnO:.3-.4 ZnO:.15-.4 NiO:about 1.0 F8203, the total mol ratio of said bivalent metal oxides to F8203 being approximately 1:1 moistening the powdered mix with an aqueous binding composition, molding the resulting plastic mix to the desired shape, firing the molded article at Seger cones 7-10 to produce a ferromagnetic molded product having a Curie point of at least 250 (3., an initial perineability of 200-350, a saturation flux density of at least 3750 and a temperature coefficient of U. of 25-35% (measured on a toroid) between room temperature and 125 C.

3. A process of making a ferromagnetic ceramic material having small magnetic losses over a frequency range of 60 cycles to 10 megacycles and a high saturation-flux density comprising the steps of grinding and mixing the metallic oxides MgO, Win02, ZnO, 'rliO, and FezOa in the mol ratio of .O -.5 MgO:.2-.4 manganese oxide calculated as lvIn :.3-.4 ZnO:.15-.4 NiO:about 1.0 FezOa, the mol ratio of the iron to the total amount of the other said metals being approximately 2:1 moistening the powdered mix with water, molding the resulting plastic mix to the desired shape, firing the molded article Seger cones 7-10 and permitting it to cool in air to produce a ferromagnetic molded product having a Curie point of at least 250 (3., an initial permeability of #0 of 200-350, a saturation flux density of at least 3750 and a temperature coefficient of p. of 25-35% (measured on a toroid) between room temperature and 125 C.

4. A process of making a ferromagnetic ceramic material having small magnetic losses over a frequency range of 50 cycles to 10 megacycles and a high saturation-flux density comprising the steps of grinding and mixing the metallic oxides MgO, M1102, ZnO, Ni(), and FezOs, the mol ratio of the iron to the total amount of the other said metals being approximatel 2:1 nioistening the powdered mix with water, adding a wax as a plasticizer, molding the resultant plastic mix to the desired shape, firing the molded article at Seger cones 7-10 and permitting it to cool in air to produce a ferromagnetic molded product having a Curie point of at least 250 0., an initial permeability of t of 200-350, a saturation flux density of at least 3750 and a temperature coefficient of n of 25-35% (measured on a toroid) between room temperature and 125 C.

ERNST ALBERS-SCHOENBERG.

REFERENCES CITED The following references are of record in the tile otthis patent:

OTHER REFERENCES Snoek: New Developments in Ferromagnetic Materials, (1947), Elsevier Publishing 00., Inc., New York, pp. 69-71. 

1. A FERROMAGNETIC CERAMIC MATERIAL CONSISTING MAINLY OF IRON OXIDE COMPOUNDS OF THE MAGNETITETYPE, SUITABLE FOR THE USE AT FREQUENCIES BETWEEN 60 CS. AND ABOUT 10 MCS. COMPOSED OF THE BIVALENT METAL OXIDES MGO, MNO, ZNO AND NIO AND FE2O3 IN THE MOL RATIO OF .05-.15 MGO:.2-.4 MNO:.3-.4 ZNO:.15-.4 NIO:ABOUT 1.0 FE2O3, THE TOTAL MOL RATIO OF SAID BIVALENT METAL OXIDES TO FE2O3 BEING APPROXIMATELY 1:1 SAID MATERIAL HAVING A CURIE POINT OF AT LEAST 250* C., AN INITIAL PERMEABILITY BETWEEN 200 AND 350, A SATURATION-FLUX DENSITY OF AT LEAST 3750 AND A TEMPERATURE COEFFICIENT OF U OF 25 TO 35% (MEASURED ON A TOROID) BETWEEN ROOM TEMPERATURE AND 125* C. 